: During development many cellular mRNA are transported from site of synthesis to the site at which they function, and play important roles in determination of cell fate, and a wide range of biochemical activities. Similarly, viral RNAs are targeted to different sites in the host cell where they may take control of cellular functions as they build the 'factories' where virus replication takes place. Often such control results in significant impact on the cell, and in some cases results in apoptosis. Intracellular transport of viral RNAs, and virus replication complexes uses many of the cytoskeletal and membrane components used by host mRNAs. However, the mechanisms of assembly and transport of complexes are not known, and if known may lead to development of chemical or protein therapies that would block virus replication and attendant disease. The research proposed here will isolate and identify the critical components of the cellular membranes that comprise the replication complex for the model plant virus tobacco mosaic virus. The P30 Movement protein encoded by the virus is responsible for recruitment of large bodies of ER membranes to establish the replication factories. After the factories are assembled the membranes are redistributed in the cell. We will identify the host protein factors and processes that are essential for establishing the virus factories and for intracellular transport of the complexes from the perinuclear region, to the cytoplasmic ER, and lastly to the periphery of the cell. Specifically this research project will: I. Determine the topology of the P30 protein in the anchoring viral RNAs; II. Determine the role of MP sequences in aggregation of cellular membranes and for anchoring viral RNAs; Ill. Identify host proteins in membrane bound replication complexes that may be involved in intracellular targeting of viral RNA; IV. Identify and isolate host genes that are essential for function of the MP for intracellular and intercellular transport of RNA, using Arabidopsis thaliana as a model system. These studies will lead to a greater understanding of transport and targeting of RNA complexes within cells, and will increase understanding of regulation of cellular processes. As the system being used involves a virus model system, the knowledge gained by this research may lead to novel therapies and transgenic approaches to control virus replication and disease.